Warren Buffett, one of history's most successful investors, put it bluntly: "The biggest decision of your life will be who you choose to marry."¹ He emphasized this during a conversation with Bill Gates at Columbia University: "You want to associate with people who are the kind of person you'd like to be. You'll move in that direction. And the most important person by far in that respect is your spouse. I can't overemphasize how important that is."¹ This isn't romantic sentimentality—it's...